lect 4 polymer synthesis ch 3 pt1.2014 (1)

8/12/2019 Lect 4 Polymer Synthesis Ch 3 Pt1.2014 (1)

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Polymer Synthesis

" I am inclined to think that thedevelopment of polymerizationis perhaps the biggest thing thatchemistry has done, where it hashad the biggest effect on everydaylife

Lord Todd, 1980

[ C H2 C H 2 ]nMagic ?

Ethylene PolyethyleneCH

2= CH

2


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Polymer TypesCarothers: ..most polymerscould be classified according tothe mechanism of polymerization,

Condensation Addition

. or the kinetics of the reactions.

Step-growth Chain

.based on Synthesis .

Condensation reactions,Nylon (1938)


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Types of Reactions

Condensation

Addition

Ring opening

Nylon 6,6

Polyethylene

Nylon 6

H 2 N (CH 2 )6 NH 2 + HO C (CH 2 )4 C OH

OO

CH 2 CH 2

N

CO

H


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Condensation Reactions(Small molecules)

Acetic Acid Ethyl Alcohol

ReversibleReaction!

Ethyl Acetate

Ester linkage

CH 3 C OH + CH 3 CH 2 OH CH 3 C O CH 2 CH 3 + H 2 O

O O

Reactants with a functional groupMono-functionalStep-wise reaction.

H2O by-product.


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....produce a more stable state.

HO CH 2 CH 3

Acetic Acid

Reaction intermediate

Ethyl Alcoholor Ethanol

CH 3 C OH

O


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Reaction: cat. by acid and higher temps.

Heating to just over 100

C,-gets the reaction going, drives off water,

Step-wise reaction1st step: addition reaction (rev.)2nd step: product formed; water eliminated (rev.).

Why doesnt it form a polymer?

Acetic Acid Ethyl Alcohol

ReversibleReaction!

Ethyl Acetate

Ester linkage

CH 3 C OH + CH 3 CH 2 OH CH 3 C O CH 2 CH 3 + H 2 O

O O

Carboxylic acids react withalcohols to form esters


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Producing a PolymerMono-functional molecules: undergo only one step;

produce small molecules

Bi-functional molecules: each product can react again;

produce linear chains;

The reaction proceeds step-wise!

+


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First step towards a Polyester

Dimer?

Monomers

HO C (CH2)

n C OH + HO (CH

2)

m OH

O O

HO C (CH 2 ) C O (CH 2 )m OH + H 2 O

O O

Bi-functionality is retained through-out the polymerization;

This is the first repeat unit (AB). Is it a copolymer?


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Step-Growth Reaction

H 2 O

Trimer M 1 + M 1 M 2 M 2 + M 1 M 3

M 2 + M 2 M 4

M 3 + M 1 M 4

M 4 + M 1 M 5

M 3 + M 2 M 5

M 5 + M 1 M 6Etc.

HO C (CH 2 )n C OHHO C (CH 2 )n C O (CH 2 )m OH +

O O O O

HO C (CH 2 )n C O (CH 2 )m O C (CH 2 )n C OH

O O O O

This is the ABA,or half-way tothe AB dimer.


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Step-Growth Polymerization;Summary


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First polyesters had low MWs, low MPs.(


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Nylons (Polyamides)

Adipic Acid Hexamethylene Diamine

Amide Group

H 2 N (CH 2 )6 NH 2 + HO C (CH 2 )4 C OH

O O

H 2 N (CH 2 )6 N C (CH 2 )4 C OH + H 2 O H

O O

Condensation reaction: proceeds step-wise,rev. steps, elim. water.

Reactants: carboxylic acid plus amide.

AB with asymmetricreactive ends.


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Nylon 6,6

n

6

Amide Group

6

O O

N (CH 2 )6 N C (CH 2 )4 C O

H

H

-Several nylons.-Structures vary by the number of

(CH 2) groups between the amide linkages;6,6; 4,6; etc.

- Basic repeat unit has two different mers.

Error: N not O


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Ad. from N.Y. Herald Tribune,Oct. 30 1938

I am making theannouncement of a brandnew chemical textile fiber ---

derivable from coal, air andwater -- and characterized byextreme toughness andstrength --

Charles Stine V.P. forresearch, Du Pont, 1938

Biggest initial impact on products forthe military and stockings .


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Post WWII stocking sale, San Francisco.

Find Waldo.


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Stoichiometry Issue

The reaction requires equal molar amts of the monomers.. . . not an easy on an industrial scale.

Trick with nylon: pre-prep the acid:amine salt, precipitates as a 1:1 complex .

Nylon Salt

OOC (CH 2 )4 COO

+ NH 3 (CH 2 )6 NH 3 +


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Nylons (Polyamides) From Diacyl Halides

Adipoyl Chloride Hexamethylene Diamine

Amide Group

Is a water molecule always eliminated?

H 2 N (CH 2 )6 NH 2 + Cl C (CH 2 )4 C Cl

O O

H 2 N (CH 2 )6 N C (CH 2 )4 C OH + HCl

O O

H

HCl is driven off, drives the reaction, makes it irrev.


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Hexamethylene diaminein water

Adipoyl chloridein chloroform

Nylon 6,6 formedat the interface

Nylon "skin"

carefully drawn offto form fiber or rope

The Nylon Rope Trick

What about the stoichiometry in the reactor?

Forms amide bond;HCl byproduct


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O C N (CH 2 )6 N C O + HO (CH 2 )2 OH

Polyurethanes-Bi-functional monomers-Addition reaction-No small molecule eliminated.

Hexamethylene Diisocyanate Ethylene Glycol

Urethane Linkage

O

H O C N (CH 2 )6 N C O (CH 2 )2 OH

R-N=C=O from the dehydration of R-NH-COOH .


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Polyesters From Diesters

+ 2CH 3 OH

Dimethyl Terephthalate Ethylene Glycol

CH 3 O C C O CH 3 + 2(HO (CH 2 )2 OH)O O

C O CH 2 CH 2 OHHOCH 2 CH 2 O C

O O

COOH was converted (activated) to an ester group.Ester monomer produces ester polymerMethanol by product


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+ HOCH 2 CH 2 OH

Polyesters from Trans-esterification

Transesterification

And so on


O O


O O

C O HOCH 2 CH 2 O C

O O

C O CH 2 CH 2 OHCH 2 CH 2 O C

O O


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Summary of Polymerization Reactions

Addition Condensation*

Chain reaction Initiator Double bond present in

monomer Single monomer No by-products Few long chains; no

double bonds Branching possible

Step-wise reaction H+ Initiator Bifunctional monomers 2 different monomers 2 mer repeat unit By-products Oligomers Branching is unlikely

lect 4 polymer synthesis ch 3 pt1.2014 (1)

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